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Old December 23rd 06, 04:34 AM posted to rec.radio.amateur.antenna
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First recorded activity by RadioBanter: Nov 2006
Posts: 15
Default Question about 20-meter monoband vertical (kinda long - antenna gurus welcome)

Hello all - I hope someone can help me figure this one out:

I just put up a 20 meter monoband today. Been working on it for
a week of nights, and got it in the air when I got off work today early.
I used the 234/f formula and cut it for around 14.100 mHz which
gave a length of 16 feet 7 inches. It was a a bear to hoist
up (my XYL helped me) - the base is only about 12 feet off the
ground (my only mounting option). I put up 4 identical-length
radials, 3 of which are quite close to 45 degrees, the 4th is is
only about 10 degrees down due to mounting issues. The coax
feed is about 40 feet (RG-58 - good quality). I wound a
4" form with 10 turns at the base of the antenna and another 10 turns
at the transmitter to try to keep the feed line 'out of the loop' (is this
wrong?)

I find it is REALLY broad - is this normal for a monoband? I
have only used trap verticals before. The SWR is 1.5:1 from
14.025 up to around 14.200 - very little change. It is actually
hitting resonance somewhere around 14.600 (using MFJ meter
when out of band). (See 'Problem' below)

Construction: Copper water pipe, 10' of which is 3/4" then 5' of
1/2" and finally a 1/4" section that is the 'tuning end'. For the radials,
I made a circle of 14-ga antenna wire around the 2x4 wood support
on brass hooks (one each side) that support the radials - diameter of the
radial 'circle'
is about 6" or so - not very large circle. Radials were cut exactly the
length of the antenna and are well insulated with ceramic eggs and poly
line, angles as stated above. Copper element is suported by 1.5"
ceramic stand-off insulators from the Oak + 2x4 treated wood support.

Problem: My TS-440s (AT) without the tuner only puts out
about 60 watts in CW and RTTY segments, and only hits
full power in the upper end of the SSB band UNLESS I use
the internal tuner - then I get a full power output in CW since
the transmitter is 'faked' into believing it is resonant. During my late
night (illegal 30 second) test, I get 110 watts at 14.600 with almost
no visible SWR - clearly the resonant frequency...

Questions:

Question 1: Are mono-band verticals always this broadbanded
or do I have something wrong? It does not seem to have much Q.
SWR only very slowly creeps up over the band... (I loaded at
power at 14.600 VERY FAST late at night - please don't give me
a ticket Mr. FCC! - and the SWR was almost unreadable it was
so low - the MFJ meter is right - that is my resonance point). My old
4BTV was 'sharp as a tack' in tuning... VERY high Q. Are mono-bands
less selective?

Question 2: Am I being overly concerned? I can use the Auto Tuner
in the TS-440 to make it happy without any problem... is this ok?

Question 3: I built this antenna to be good for my Oak Hills QRP rig -
I had hoped not to have a tuner in the loop - I use a Kenwood AT-180
when I'm not on the TS-440s - is the loss that significant? Again, am I
being
overly concerned, since the AT-180 very easily tunes out the difference?
Or should I tweak on this antenna until it is perfect for CW SWR?

Question 4: I understand the radials are a major part of the design - could
it
be that the 'formula' (234/f) was correct, but somehow my radials are a bit
off
and could make the difference without adjust the 16' 7" vertical length?

Question 5: Since I made the 'radial circle' about 6" diameter around the
base
of the antenna, but then connected the radials (cut exactly the length of
the
radiator, less the 'radial circle' of wire around the base, attached to the
brass
hooks used to support the radials) could this be de-tuning the antenna enuf
to
raise the frequency (seems it should LOWER in frequency if anything)?

If you 'wiser' hams advise, I'll certainly drop the antenna (after cutting
the radials
loose) and enlist my XYL to help again, and add a couple of inches of
copper to
the ends (and too the radials) and do it all agin... but it was not easy to
do in the
first place... (The antenna only weighs 25 pounds, but OMG lifting it up to
position
felt like it weighed 250 pounds!!)

How it performs: I found during on-the-air tests that SOME signals were
significantly
better over my 200' "random wire" and some were worse. Consensus was that
there
was almost no difference 'short haul' (coast to coast). Some signals are
not at all
audible on my 200' wire, but S7 on the vertical, for example... no DX today
so no
idea if the low angle is working or not...

But what about at QRP levels? With my AT-180 tuner? Just seems that I
should hit
my ideal SWR in the 14.060 range - rather than 14.600 despite the broad-band
performance.

What do you recommend I do at this point? I have the whole weekend to
either play with the
new antenna or quit obsessing over it :-)

Thanks for replies and putting up with my long-winded posting. Please
either post here
or at my email address of

many thanks,

Dave WB7AWK


 
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